JP Patent Publication 2005-249003A discloses a rotation transmission device used in an FR-based four-wheel drive vehicle for selectively transmitting driving force to the front wheels as auxiliary drive wheels.
The rotation transmission device disclosed in JP Patent Publication 2005-249003A includes a two-way clutch disposed between a large-diameter portion of an input member and an outer ring provided therearound, and an electromagnetic clutch provided beside the two-way clutch for selectively engaging and disengaging the two-way clutch, whereby when the two-way clutch is engaged, the input member is coupled to the outer ring, so that torque is transmitted between the input member and the outer ring.
The outer ring of the two-way clutch has a cylindrical surface on its inner periphery, while cam surfaces are formed on the outer periphery of the large-diameter portion of the input member to define wedge-shaped spaces that narrow toward their circumferential ends between the cylindrical surface and the respective cam surfaces. The two-way clutch further includes engaging elements in the form of rollers mounted between the respective cam surfaces and the cylindrical surface, and a retainer retaining the engaging elements. When the retainer and the input member rotate relative to each other, the engaging elements are adapted to engage the cylindrical surface and the cam surfaces. The two-way clutch further includes a switch spring mounted between the input member and the retainer that biases the retainer to keep the engaging elements in neutral positions where the engaging elements are disengaged from the cylindrical surface and the cam surfaces.
The electromagnetic clutch comprises an armature rotatably fixed to the retainer so as to be axially movable, a rotor connected to the outer ring and axially facing the armature, an electromagnet axially facing the rotor, and a separation spring biasing the armature away from the rotor, whereby when the electromagnet is energized, the armature is attracted to the rotor, and the engaging elements engage the cylindrical surface and the cam surfaces due to rotation of the armature, which is now coupled to the outer ring, relative to the inner member.
With this two-way clutch, because the rollers are moved from the wide portions of the respective wedge-shaped spaces to one of the narrow ends of each wedge-shaped space when the input member and the retainer rotate relative to each other, play in the rotational direction is large.
Also, when changing the direction in which torque is transmitted between the outer ring and the input member, it is necessary to rotate the retainer until each roller wedges into the opposite narrow end of the wedge-shaped space. Thus, it is impossible to quickly change the rotational direction.
To avoid this problem, JP Patent Publication 2003-262238A proposes to arrange the rollers at unequal intervals such that one and the other of each adjacent pair of rollers are located at one and the other ends of the wedge-shaped spaces.